The expansion of an underground mine (e.g. a coal mine) requires digging a tunnel which initially has an unsupported roof. To stabilize and support the roof a roof bolt must be inserted into the roof to provide support. The operator must first drill holes in the roof through the use of a rotatable cutting bit or roof drill bit. A roof bolt is then inserted into each one of the holes.
A common roof drill bit design uses a cutting insert that has been brazed into a slot at the axially forward end of the roof drill bit body. U.S. Pat. No. 5,400,861 to Sheirer discloses various roof drill bits. U.S. Pat. No. 4,603,751 Erickson also discloses various roof drill bits. Applicants hereby incorporate U.S. Pat. No. 4,603,751 and U.S. Pat. No. 5,400,861 by reference herein.
In addition, the following catalogs published by Kennametal Inc. of Latrobe, Pennsylvania (U.S.A.), which are hereby incorporated by reference herein, disclose roof drill bits: "Kennametal Mining Products", Catalog A96-55(15)H6 (September 1996) [36 pages in length], and "Kennametal Mining Products" Catalog B92-75R(3)M5 (1992) [36 pages in length].
Other United States patents that disclose roof drill bits and cutting inserts for roof drill bits include U.S. Pat. No. 4,489,796 to Sanchez et al., U.S. Pat. No. 4,527,638 to Sanchez et al., U.S. Pat. No. 4,787,464 to Ojanen, U.S. Pat. No. 5,172,775 to Sheirer et al., U.S. Pat. No. 5,269,387 to Nance, U.S. Pat. No. 5,375,672 to Peay et al., and U.K. Pat. Application No. 2,280,627 to Peay et al.
While some of the earlier roof drill bits provide acceptable performance characteristics, there remains the desire to improve upon these characteristics. In this regard, roof drill bits which have a higher penetration rate for the drilling operation are desirable because it typically takes less time to drill the required number of holes in the mine roof (i.e., earth strata) with such a roof drill bit. A roof drill bit which uses a cutting insert wherein the cutting insert is of a design so as to reduce the resistance to penetration enhances the potential to maintain a higher penetration rate at a given thrust level for a longer time.
It thus would be desirable to provide an improved roof drill bit, as well as an improved cutting insert for the roof drill bit, that has a high penetration rate wherein such roof drill bit uses a cutting insert of such a design so as to reduce the resistance to penetration during the drilling operation.